Topic: cb750 increasing alternator output voltage a low RPM

[2wheels]

I have read posts about wanting to increase the alternator output voltage while idling.
I am a electrical technologist so I know a little about some electrical equipment not not much about alternators or motors.

I wonder if it is possible to get more voltage out of the alternator ,while idling, by increasing the field voltage up to something like 15 volts.  Or whatever until you reach the maximum field current.

Use a boost power supply like
https://www.amazon.ca/DROK-Transformer-Controller-Stabilizer-Automotive/dp/B00BXDH9A2/ref=sr_1_4?ie=UTF8&qid=1515607847&sr=8-4&keywords=15+volt+dc-dc+converter

Install this power supply (that can take an input voltage of say 11 volts and increase it to 15 volts)  just before the regulator.  So it is only supplying the alternator field circuit.
I expect it would work as planned, but not sure if the increase you would get would be worth the effort.
Comments

[strynboen]

there is nothing like free energie..
.

..you need thikker viring in the stator..or longer vire..or just more vire..that is the only vay to pump more jouce aut..

[2wheels]

I don't think it is free energy.  Just more voltage produced at low RPM.


Rewiring the stator is necessary if you need more power from the alternator.  Not what I am talking about.

[Jerry Rxman Griffin aka MuthaF'er]

Figure out a way to set up the 750A field coil and stator.

[Don R]

 I'd guess a solid state voltage regulator would help, along with optimizing the connectors to minimize loss would be a good start.

  I can't help with your idea though, my question would be how would doing that affect voltage at higher rpm's?

[2wheels]

As I said, this is not my field.  So I am only guessing.

I was just looking at the circuit with the mechanical regulator, like my bike has.  I don't think my idea would work with this.
It would need to be more complex.

But the question I have still remains.  Could the alternator make more voltage at idle, if the field voltage can be increased.
Thanks for the comments.

[Bodi]

Yes. More field voltage = more field coil current = more magnetic field = more stator coil current out.
More voltage - I don't know, the alternator is a current source and the stator coils open circuit voltage is not very important.
But it may be a losing proposition, the output current increase may be less than the increase in field current. And the field coil will eventually overheat.

[Jerry Rxman Griffin aka MuthaF'er]

And as I said, "Figure out a way to set up the CB750A field coil and stator". They have an output of 285W vs the F and K output of 225W. This is achieved through the change in the windings/gauge of wires. This will increase your field strength and I would expect this throughout the rpm range. This is also similar to what Strynboen is suggesting without the rewinding.

There are also other "cures" that have been discussed here but I'm thinking the search function is down again. Aftermarket regulator/rectifier units, build your own R/R, complete adapted systems.

As Don suggests a solid state R/R MIGHT help. Also a new wiring harness or rebuild your's with new connectors. Maybe you are getting loss at the key switch? Anyway these are things that will help an ailing system and you haven't stated your's is ailing or provided any symptoms.

The OLD electrical system is probably the biggest pain in the ass of the 750.

Good luck 

ps just caught Bodi's post. You need power not voltage in all likelihood and a low voltage is a symptom of a problem. Increasing voltage IMO is not the cure you need.

[2wheels]

Good point about the current used by the field may be more than the stator produces.
I dont have a problem with my bike, i would say it is normal.   And i dont idle a lot.  I was just wondering if there was an easy fix for the low voltage while idleing.  Not that it is a big problem.

It is winter here, lots of snow.  Whats a biker to do?

[Yamahawk]

Volts*Amps=Watts. If you increase Volts, your Amps decrease. There is no free electric, unless you find out the resonant frequency of the electrolyte in your lead acid battery, and pulse the battery at a frequency that will ring it like a bell (resonance), providing an increased output while pulling your electrical load... similar to the desulfator circuits out there that splits the lead and sulfuric acid back into the battery. Now, there is a way to do this, and it has been documented... Good luck in your search for that one! However, that is not the solution to your increased voltage to the field coil.
"Wait a minute... the solution's turning blue! Not quite the solution I expected. That means the Cat should have lived, and the Rat should have died..... Of course!" Hemlock Stones, Tale of the Giant rat of Sumatra. (The Firesign Theater)
Charlie

[HondaMan]

You can gain a little bit more (about 250w over the stock 210-225w) by just using a CB750A field coil, no other change needed. That's the old chopper 'hop-up' for running dual headlights, and the like. To get the full 285w of the "A" you will have to swap the alternator windings, too, and use an electronic regulator like Honda's own for that bike, or another one.

If you just want to raise yours a little bit as-is, you can just readjust the regulator.

This all said: the #1 cause of lower-than-expected power from the 750 alternator comes from just one source: the 3 zinc-plated, undersized (3.5mm) bullet connectors that tie the windings to the big plug at the back of the engine, and the big plug's connectors. The bullet connectors lost their zinc about 10 years ago, and are probably burned now: I swap them to the larger 4mm brass ones from Vintageconnetions.com instead, and replace the blades and receptacles in the big connector as well. This always raises output by a couple of amps when those little bullets are burnt. The 750 seldom suffered low-battery troubles unless someone installed extra lighting, a heated vest or Hippo Hands (Vetter) and then rode mostly in traffic at low RPM (hint: this also fouls sparkplugs - this is a high-RPM engine...).

[TwoTired]

I actually thought of the same thing a few years ago.

I do believe the higher voltage to the field coil will result in higher output from the alternator's stator.

However, the field coil's fixed resistance will also make it consume more current/power, robbing at least some of the output power gains.  And I fear that the heat generated will damage the filed winding insulation.  This later, and having a field coil that already shorted itself out due to fail winding insulation, made me less enthusiastic about implementation.

750 has a 6.8 ohm field coil, which consumes 1.8 amps (21.6 watts) with a 12 volt input, and 2.20 amps (33 watts) with a 15V input.  Maybe need to add cooling fins to the field coil cover.  I'd want to do some temperature testing.

I also decided that it wouldn't be a good thing to overwork the alternator field all the time, only during times when the load exceeded the generation capacity.  This would necessitate some added circuitry, for regulation, switchover to the 12V.

Then, since I really didn't have a need for more power output, I worked on something else. 

Cheers,

[754]

The A stuff should bolt on but i think the rotor may be longer .
 The Hippo Hands are they electric ? I thought just covers..

[Yamahawk]

The A stuff should bolt on but i think the rotor may be longer .
 The Hippo Hands are they electric ? I thought just covers..

They have an electric option now! Not back when I was using them, but there are plugins now lol.
Charlie

[PeWe]

Stock charging system work fine as long it is OK, regulator adjusted if needed. A CB750 will be used above 4500 rpm most of the time.

If Idle a lot use a headlight with parking as the EU bikes got.

Other problem with excessive idling is overheating engine wich should be more important to care about.

[scottly]

Install this power supply (that can take an input voltage of say 11 volts and increase it to 15 volts)  just before the regulator.  So it is only supplying the alternator field circuit.

Just for the sake of discussion, if the voltage booster was installed between the black harness wire and it's terminal on the reg, the reg would see a 15v reference, and thinking the voltage was too high, wouldn't send any current to the field, so no charging would happen.

[scottly]

There is no free electric, unless you find out the resonant frequency of the electrolyte in your lead acid battery, and pulse the battery at a frequency that will ring it like a bell (resonance), providing an increased output while pulling your electrical load...

You're joking, right?

[Don R]

 I'd say yes about the joking.

 I was told a 6 volt bike may be converted to 12V by changing the battery and V reg/rec. I did it on a cl100 but also changed to a 12v stator from a cb360. It was working awesome when I sold it.

 That may be a clue to the original question.

[strynboen]

you can go the Kawasaki vay...split the rotor..put a strong magenet inside.(.drop the elektromagenet.)..and then use the "rest to frame" reg..Suzuki use the same...only dravback is that it sucks a lot of mecanicc powern from the engine ..even at full loadet battery..so you Loose a few hp..

still Hondas system vith elektromagenet is the best vay to turn off a generator..just like a elektric clutch on a aircom pump(or almost),,as the Honda can run all step of power needet..full variabel...vill be a shame to Loose that..

[Yamahawk]

There is no free electric, unless you find out the resonant frequency of the electrolyte in your lead acid battery, and pulse the battery at a frequency that will ring it like a bell (resonance), providing an increased output while pulling your electrical load...

You're joking, right?

Actually...no. I am not joking. You can do it mechanically with a three brush setup on an armature off the motor shaft that has a conductor a little less than half of the circle, fed with the 1st brush, the other 2 brushes opposite each other, with one of the brushes timeable like the points on a points plate... you pass the one brush to the DC motor, running it off pulsed DC, the other timeable brush goes to  6 coils of 200 turns on enameled magnet wire wrapped on a core (bolt), with a disc with 6 permanent magnets spinning on the end of the extra long motor shaft shimmed to the cores. This increases your voltage, and sends it back to the battery. By hooking up the two brushes to the A and B channels of an oscilloscope, you 'time' the pulse to around 1-2 MHz, and when you find the resonance of the electrolyte, it will charge the battery, pull the load and continue until the battery boils dry... which then you need a VR to regulate the battery charge in that line.
Now, I expect a little bit of skepticism in this, but the study of resonant frequencies is most amazing, and what they can do. This is but one example! You can do it with a 555 timer circuit also...
Charlie

[2wheels]

Just for the sake of discussion, if the voltage booster was installed between the black harness wire and it's terminal on the reg, the reg would see a 15v reference, and thinking the voltage was too high, wouldn't send any current to the field, so no charging would happen.

True.  The mechanical regulator would not work.  As TT says a circuit would be needed to switch in the power supply voltage when it detects the motor is idling.  In the normal , driving mode, the regulator would be used .  So a relay between the field coil and regulator, and a circuit to control it.

[2wheels]

So , if i don't want to modify the bike to much.  and I don't want to burn the field coil up.  then I cannot do what I was thinking.

I won't touch the resonance idea, even if it works.  The resonant frequency changes with every possible factor, temperature , any change in the battery state, liquid level.  Very difficult to control.   Some of us are already uncomfortable with a battery between or legs.  Never mind giving the battery a good excuse to explode.  ( i do like out of the box ideas, so thanks for that)

Maybe a bunch of peltier junctions fixed to the exhaust headers.  Now that would be free energy.  It would make a lot more power while driving than idling though.

[Yamahawk]

So , if i don't want to modify the bike to much.  and I don't want to burn the field coil up.  then I cannot do what I was thinking.

I won't touch the resonance idea, even if it works.  The resonant frequency changes with every possible factor, temperature , any change in the battery state, liquid level.  Very difficult to control.   Some of us are already uncomfortable with a battery between or legs.  Never mind giving the battery a good excuse to explode.  ( i do like out of the box ideas, so thanks for that)

Maybe a bunch of peltier junctions fixed to the exhaust headers.  Now that would be free energy.  It would make a lot more power while driving than idling though.

Now you're thinking! The heat from exhaust could be used in a lot of different ways... at one time, I figured out a way to eliminate the compressor on automotive A/C systems, freeing up extra horsepower, by using a heat exchanger ion the evaporator tank, running the exhaust pipe through a double wall system that would heat the freon, expanding it to create the compressor effect. Back in the day, Hamilton built freezers that ran off of a pilot light to heat the expansion tank, and so do RV refrigerators. So, why couldn't car manufacturer's do the same thing with the free heat from their engines? No moving parts, and they would work fine if non-corrosive metals were used in the heat exchangers, and using exhaust cut out valves.... but, I digress, once again. Sorry fellas.
The idea of varying the voltage on the field coil is exactly what the system does now, and like Hondaman said, simply adjusting the regulator for a little more output will do the trick.
Charlie

[strynboen]

here is the hardvare..in different load modes...

[TwoTired]

Now, I expect a little bit of skepticism in this, but the study of resonant frequencies is most amazing, and what they can do. This is but one example! You can do it with a 555 timer circuit also...
Charlie

I find there is good reason for skepticism.  Applying frequencies to a battery for desulphation, and for that matter any resonance technique, can only apply to one or perhaps two cell batteries.  Any pulses applied to the battery are damped greatly by the capacitive action of the battery plates.  Resonance relies on the capacitance value (frequency, Induction, and resistance, too).  A six celled battery has the cells arranged in series. To get frequencies or quick rise time pulses to the inner cells, the resonance frequencies or pulses must pass through the outer cell's huge capacitive value, which will alter the frequency profile significantly outside of resonance.  Therefore, the inner cells have no hope of receiving an applied resonance or desulphation pulse.  Only plates that are in direct connection with the driving circuit have any hope of experiencing a resonant or pulse benefit.

I believe battery chargers that promote sales using desulphation circuitry are just razzle dazzle to beguile prospective buyers.  These chargers will still charge a battery by presenting a potential voltage difference to the cells.  Pulses are fine as the battery will just average out the presented pulses.  But, significant desulphation?  Better hope all your major sulphation is in the outermost cells.  The inner cells will exhibit some desulphation each time a simple DC potential applied to them, as long as they can pass any sort of current.  That is a basic function of the battery chemistry.  Getting fast rise time pulses, or resonance to the inner cells without special connection construction of the battery, just isn't physically or electrically possible.

Food for thought...

Cheers,